1. Field of the Invention
The present invention is related to the field of fuel control systems for providing metered quantities of fuel to a power producing engine. More specifically, the present invention is related to that portion of the above-noted field in which fuel is provided in response to accurately timed electrical pulses. More particularly, the present invention is related to that portion of the above-noted field which is concerned with the generation of the accurate electrical pulses. In particular, the present invention is related to that portion of the above-noted field in which an electrical pulse is generated during the period of time that at least a portion of a controlled voltage waveshape maintains a selected relationship with respect to a selected value. The present invention is specifically related to that portion of the above-noted field in which the controlled voltage waveshape has a first portion for introducing a control parameter and a second portion following immediately thereon for controlling generation of the electrical pulse. In a fuel control system in which the electrical pulses are generated while the second portion of the waveshape remains below a threshold value, the present invention is concerned with providing continuously variable control of the first portion of the waveshape to modulate the initial value of the second portion to thereby controllably affect the period of time that the second portion remains below the threshold value.
2. Description of the Prior Art
My co-pending commonly assigned patent application Ser. No. 219,275 entitled "Circuit For Providing Electronic Full-Load Enrichment Fuel Compensation In An Electronic Fuel Control System" filed on Jan. 20, 1972, describes one method by which the initial value of the second portion of the controlled voltage/waveshape may be modulated. The method shown and described therein is adequate provided no more than two levels of controlled voltage are desired and further provided that the corrective factor is changing from a lower to a higher value for decreases in engine rpm. By "corrective factor" or "correction factor" is meant that value which the first portion of the controlled waveshape must maintain for various rpm values to provide an initial value to the second portion of the controlled waveshape to produce an output electrical signal of a duration which is accurate for the engine speed.
If greater numbers of different corrective factors are required, or if the sequence of corrective factors does not permit a continually increasing or continually decreasing corrective factor for changing engine speeds the circuitry illustrated in my co-pending application is not effective. Furthermore, using the design philosophy embodied in that circuitry would require extensive additional circuitry to add in additional corrective factors even for smoothly varying factor changes. It is therefore an object of the present invention to provide circuitry for generating rpm corrective values which may have a plurality of stable or uniform levels and which may switch between the various levels in response to variations in engine speed. More particularly, it is an object of the present invention to provide such a system which is capable of providing three or more corrective factor levels in a simple and easy to implement fashion which will not unduly burden the electronics of the system. It is a still further object of the present invention to provide such a system in which switching between the various corrective factor levels may be readily accomplished irrespective of the sequence of change of the corrective factors.
An associated problem which has been treated in my co-pending commonly assigned patent application docket number MOC 70/75 and titled "RPM Information Signal Generating Circuitry for Electronic Fuel Control System" had to do with the generation of knowledge as to the precise engine speed. The solution to this problem resulted in the design of electronic circuitry which would respond to engine speeds by determining whether or not the period of time following an engine triggering event was shorter or longer than the time period associated with engine speed at selected rpm values. By "triggering event" is meant the signal, or the condition of engine operation giving rise to the signal, which is used to indicate at least one selected angle of engine crank shaft rotation. With the capability of generating rpm information as one or more electrical signals whose presence or absence could be interpreted to yield a range of speeds within which the instantaneous engine operation would exist, it therefore becomes an object of the present invention to provide electronic circuitry which is capable of receiving such information and generating the desired corrective factors as a function of the information received. In view of the fact that it has been determined that accuracy considerations require nearly current rpm information it is also an object of the present invention to provide circuitry for continuously generating an accurate correction factor in response to a signal or signals indicative of engine speed.